Adhesive Tiecoat/Polyimide Interactions in High-Temperature Flex Packaging

Authors: Harry Schoeller and Junhyun Cho, Binghamton University; Aaron Knobloch, Dave Shaddock, Xia Hua, Kevin Durocher, and Chris Kapusta, General Electric Global Research.

Venue: ASME InterPack ‘07, The Westin Bayshore, Vancouver, BC, Canada, July 8-11, 2007, (http://www.interpackconference.org/interpackhome.html) [external site]).

Abstract: The high-temperature reliability of flex-based Cu/tiecoat/polyimide structures was evaluated through finite element simulation and an experimental approach. This study is part of an effort to characterize and optimize polyimide flex as a substrate material for electronics packages rated to greater than 204 °C. The peel strength of several common adhesion metals (Ti, Cr, Ni, Cu) on Kapton E was quantified at room temperature and after high-temperature storage in inert and highly oxidizing environments. These results were used in tandem with thermal-mechanical simulations to characterize the behavior of several tiecoat materials. Experimental results showed diminished peel strengths of both the Ti and Cr after a 100-hour, 250 °C heat treatment in air. However, when annealed in an inert N₂ environment at 250 °C for 100 hours, Cr, Ni, and Ti retained their as-sputtered peel strength. Ni and Cu exhibited lower mechanical stresses in the simulation; however, their relatively low reactivity limited their adhesion strength at the interface in oxidizing environments. To further understand the origin of the thermal-mechanical stress, the effect of mismatched CTE was compared with mismatched elastic modulus. Both properties were found to contribute to stress generation; however, elastic modulus mismatches had a much greater influence on the overall magnitude of the stress. Through experimentation and finite-element analysis this study aims to develop a flexed-based, high-temperature packaging solution and to shed light on high-temperature tiecoat/polyimide interactions.

Related NETL Project: The overall objective of the related NETL project DE-FC26-06NT42950, “Harsh-Environment Electronics Packaging for Downhole Oil & Gas Exploration,” is to develop new packaging techniques for downhole electronics that will be capable of withstanding at least 200 °C (~400 °F) while maintaining a small-form factor and high vibration tolerance necessary for use in a downhole environment. These packaging techniques will also be capable of integrating a sensor and other electronics to form an integrated electronics/sensor module.

NETL Project Contacts
NETL – Gary Covatch (gary.covatch@netl.doe.gov or 304-285-4589)
GE Global Research – Aaron Knobloch (knobloch@research.ge.com or 518-387-7355)